The present invention relates to a tire tread support device, said device being used in the event of the travel of the tire under an inflation pressure of zero or low value. The use of such a device, also known as safety device, mounted within the tire is to permit an equipped and loaded vehicle to continue to travel despite the partial or total loss of inflation pressure, the continuity of travel being beneficial for various obvious reasons.
Metal safety devices are widely known. In the event of the use of such devices in combination with tires intended for and capable of traveling on various soils, comprising, in particular, stones, rocks or various agglomerates, said devices do not withstand impacts well and are fragile, their rupture leading rapidly to the complete destruction of the tire.
There are also known safety devices which are made of rubbery elastic material, that is to say of a vulcanized mix composed of natural or synthetic rubber, reinforced by known reinforcement agents in the presence of the necessary additives. These devices are entirely suitable for supporting a small load, for instance in the case of tires of a passenger vehicle. On the other hand, in the case of tires which support heavy loads, the weight and the hardness properties of the vulcanized mix which are necessary to support the load with a reasonable yielding of the tire are such that the travel of the assembly results rapidly and prematurely in a heating which is not compatible with the life of the tire.
European Patent 0 130 136 describes a safety device formed of two different materials: the radially inner part or support of said device, which is rigid, is made with any rigid material, in particular a reinforced plastic or metallic material, and the radially outer part or cap, which is not rigid, is formed of any vulcanized elastomer. These two parts, namely support and cap, are connected together firmly in such a manner that they are made incapable of any relative movement with respect to each other.
The device described is likewise made integral with the mounting rim, a lubricant being employed in order to lubricate the interface, in the case of travel under low or zero pressure, between the radially outer face of the cap and the radially inner face of the crown of the tire. The cross-sectional height of the device can be between 25 and 55% of the height of the tire, seen in meridian section. As to the cross-sectional height of the support, it may be between 20% and 80% of the height of the device.
As the safety devices are frequently used on vehicles which have a "centralized" inflation system, that is to say a system which permits the inflating of the tires while traveling, the lubricant, which is arranged on the cap and is dispersed under the effect of the rubbing and heat, can easily discharge through the inflation conduits and clog them. Furthermore, the presence of the lubricant does not do away with the coefficient of rubber-on-rubber friction and the friction is still substantial.
It is also known that it is possible and preferable that the safety device to be able to turn around the rim so as to permit compensation for the difference in circumference between the inside of the crown of the tire and the radially outer face of the device. This is taught in U.S. Pat. No. 3,635,273 in which the means described to permit the rotation of the device around the rim concern the interface between the rim and the said device. In the case of a substantial transverse force suffered by the tire traveling under small or no pressure, such force is transmitted almost entirely to the rim-device interface, that is to say, to the level of the said means, which makes them as well as the interface fragile. They then rapidly lose their effectiveness.
In GB 2 084 088, the safety device comprises a rigid support, which is fixed with respect to the rim, over which radially on the outside, there is an elastic belt of rectangular section which is movable with respect to the rigid support and partially engaged in a circumferential groove developed on the outer face of said support; the side faces of this recess serve as stops for the axial displacements of the belt. This device has the drawback that the side edges of the rigid support can come into contact with the walls of the tire.